A display device using a plasma display panel (PDP) has recently received attention as a color display device used for displaying an image in a computer and a television, because this display device using the PDP can be large, thin, and light.
The PDP allows full color display by adding and mixing three so called primary colors (red, green, and blue). For displaying full colors, the PDP has a phosphor layer for emitting light of each of the three primary colors, namely red (R), green (G), and blue (B). Phosphor particles constituting the phosphor layer are excited by ultraviolet rays generated in a discharge cell of the PDP to generate visible light of each color.
Compounds employed for the phosphors of respective colors are, for example, (Y1-y,Gdy) BO3:Eu3+ (0≦y≦1) or Y2O3:Eu3+ for emitting red light, Zn2SiO4:Mn2+ for emitting green light, and BaMgAl10O17:Eu2+ for emitting blue light. These phosphors are produced by mixing predetermined raw materials and then by calcining them at a high temperature of 1000° C. or higher for solid phase reaction (for example, Phosphor Handbook, P219–220, Ohmsha, Ltd.). Phosphor particles produced by this calcination are crushed and classified as red and green particles with an average grain size of 2 to 5 μm and blue particles with an average grain size of 3 to 10 μm and then used.
The crushing and classification of the phosphor particles are performed for the following reason. In forming the phosphor layer in the PDP, a method of deforming the phosphor particles of each color to paste and silk-screening the paste is generally employed. A flatter coated surface can thus be easily obtained when grain sizes of the phosphor particles are smaller and more uniform (uniform grain size distribution). In other words, when grain sizes of the phosphor particles are smaller and more uniform and their shapes are closer to spherical, the coated surface is flatter, filling density of the phosphor particles in the phosphor layer increases, light emitting surface area of the particles increases, instability in address driving is improved, and hence theoretical luminance of the PDP can be increased.
When the grain sizes of the phosphor particles are smaller, however, the surface area of the phosphor particles increases or defects in the surfaces of the phosphor particles increase. Much hydrocarbon organic gas or water or carbonated gas is therefore apt to adhere to the surfaces of the phosphor particles. Especially, green phosphor composed of Zn2SiO4:Mn has defects (mainly, oxygen defects) in surfaces of crystals or in the crystals, and is apt to adsorb hydrocarbon gas or water existing in the air comparing with blue and red phosphors. Hydrocarbon gas or carbonated gas generated especially in calcining the phosphor is often adsorbed to the green phosphor during or after the cooling process in the calcining. Therefore, disadvantageously, after sealing the panel, the hydrocarbon gas is released in the panel by electric discharge and hence reacts with the phosphor or MgO to decrease the luminance, decrease a driving margin, or increase discharge voltage.
Since the conventional phosphor of Zn2SiO4:Mn has many defects near the surface, the following problem occurs. Specifically, when a phosphor layer is formed in a method of applying phosphor ink from a nozzle, an organic binder reacts with the phosphor to clog the nozzle.
The present invention addresses the problems discussed above. The defects (mainly, oxygen defects) in the green phosphor are eliminated, thereby suppressing the surface of the green phosphor from adsorbing the hydrocarbon gas or water, suppressing luminance decrease or chromaticity change of the phosphor, and improving a discharge characteristic.